This program involves a multidisciplinary approach on the study of cardiac pacemakers which have now functioned for almost seven years, significant advances have been made in patient monitoring techniques. These new monitoring techniques have enabled us to monitor such diverse functions as pace rate, cell voltage, hermetic seal integrity, cell impedance, lead impedance refractory interval, energy output, lead integrity, and the cardiac electrogram directly out of the pacemaker. The instrument used for monitoring these functions is just one simple telemetry probe that does not require direct contact with the patient or even accurate placement over the pacemaker. Patient use is smplified and it is unaffected by mechanical pressure and skin or muscle potential. In conjunction with these studies, improved methods for sensing and pacing the atrium have been developed. From the data developed thus far, the position of the pacer electrode in the atrium will have a direct effect on the ability of the pacer to detect P-waves as well as pace the atrium. Accordingly, we have devloped a new lead system capable of sensing and simulating the atria at the most optimum site, the S-A node.